In the building of large, radial truck tires, the portions of the tire band next to the beads tend to be extremely thick. This is due to the large size of the beads and consequently the large size of the bead fillers that must be placed next to the beads, as well as the many carcass plies and ply ends that surround the bead fillers.
Since the beads are formed on a green tire band in such a manner that they hang along the sides of the drum, the thickened areas of the tire band next to the bead, namely the bead filler portions, must extend around the edges where the sides of the drum meet its cylindrical surface. While these edges are rounded, their radii of curvature are too small for the bead filler portions of many large truck tires to wrap around them, without losing contact with the building drum in some locations. It is thus difficult to run a stitcher wheel over the plies in these thick bead filler areas, because they are not in firm contact with the surfaces of the building drum. Often, because of this difficulty, the stitcher wheel will not stitch the plies evenly, and there will not be a uniform layering of the tire components around the bead fillers of the finished tire.
The improved drum shoulder construction of this invention is designed to solve the problem of such thick bead filler portions not laying in firm contact with the drum during the stitching operation. On the shoulder portions of the drum segments there are provided hinged shoulder segments that drop radially inwardly to present a bevelled drum contour for supporting the bead filler portions when the drum segments are in their expanded positions. When the drum segments are moved to their retracted positions, the hinged shoulder segments are lifted to positions wherein they provide firm support for the tire carcass plies in the interval between the drum segments and the bead turnover bladders.
Hinged members on tire building drums per se are not new. The segments of expandable tire building drums have been hinged at either end to provide downwardly depending supports for the sidewalls of the tire when the drum is expanded. Such hinged supports are shown in U.S. Pat. Nos. 3,536,566 and 3,607,558. However, these supports are hinged where the tread and sidewall sections come together, rather than at the bead filler part of the tire. Also, when the supports rotate about their hinges upon expansion of the drum, the beads and bead filler portions of the tire separate from the ends of the supports and are allowed to hang freely from these ends. These supports thus provide no support whatsoever for the bead filler portion of the tire when the drum is expanded.
U.S. Pat. Nos. 3,674,604 and 3,795,564 show expandable tire building drums with hinged members located adjacent the bead portions of the tire. However, the hinged members of these drums are all parts of mechanical linkages used to expand tire building drums. In no case do they provide a bevelled corner for supporting the bead filler part of the tire about a larger radius when the tire is expanded, and their constructions and movements are completely different from those of the shoulder segments of the present invention.
Hinged members have also been employed adjacent the shoulder portions of tire drums to assist in wrapping the carcass plies around the beads of the tire, as shown in U.S. Pat. Nos. 3,237,199; 3,418,192; and 3,442,747. However, these members are positioned externally of the bead portions of the tire after the plies have been folded over the bead rings and such hinged members provide no support for the tire band upon the expansion of the drum.
Other publications that are of possible interest in showing past uses of hinged members are U.S. Pat. Nos. 3,018,518; 3,121,651; 3,121,652; 3,868,203; and 4,007,081.